In-Situ Monitoring of Thermal Annealing Induced Evolution in Film Morphology and Film-Substrate Bonding in a Monolayer MoS2 Film

摘要

We perform in-situ two-cycle thermal cycling and annealing studies for atransferred CVD-grown monolayer MoS2 on a SiO2/Si substrate, using spatiallyresolved micro-Raman and PL spectroscopy. After the thermal cycling and beingannealed at 305 deg C twice, the film morphology and film-substrate bonding aresignificantly modified, which together with the removal of polymer residuescause major changes in the strain and doping distribution over the film, andthus the optical properties. Before annealing, the strain associated withripples in the transferred film dominates the spatial distributions of the PLpeak position and intensity over the film; after annealing, the variation infilm-substrate bonding, affecting both strain and doping, becomes the leadingfactor. This work reveals that the film-substrate bonding, and thus the strainand doping, is unstable under thermal stress, which is important forunderstanding the substrate effects on the optical and transport properties ofthe 2D material and their impact on device applications.